Does anyone know where I can get some very simple to use red laser diode
module units? Essentially I want a off the shelf laser pointer that I
can power with 5v. (or some other easy to produce voltage) The
application is for a clock that will point the laser at a wall to show
what time it is. The laser will be run continuously so a lifetime of at
least 10,000 hours (1 year) is required, though a lifetime comparable to
an LED (1 million hours) would be much appreciated. I'm quite willing to
turn down the brightness to achieve this, the laser dot only needs to be
visible in indoor lighting. Furthermore it would be nice if there is a
way to PWM the laser light for brightness control, but that'd be icing
on the cake!

I've already tried the two modules from http://www.us-lasers.com/
(ordered through digikey, 38-1010-ND and 38-1003-ND) They are almost
exactly what I need except for two annoying issues. First of all they
require very precisely regulated voltage to them, I spoke to one of
their engineers and he said that their input voltage must be exactly
3.0V +- about 0.1 of a volt, doable, but a pain. Secondly the quality of
the laser dot is rather poor, it's an unfocused oval rather than a tight
round point.

Something like one of those modules but that can accept less tightly
regulation power and has a good quality dot would be perfect. Anyone
here dealt with this sort of thing before?

On Tue, Dec 20, 2005 at 10:08:22PM +1300, Jinx wrote:
>
> > Does anyone know where I can get some very simple to use red
> > laser diode module units ?
>
> Why not just hack a laser pointer ? Dirt cheap

Oh I would, but this is an art project that I've beeen comissioned to
make. So I have a budget of about $100US for the laser module but also I
have to think about the long-term maintanance of the project.
Unfortunately that means that potentially unreliable things like hacking
a laser pointer are out. It's gotta be off the shelf and documented, so
that in 10 years when the laser craps out it'll be easy to replace with
another one.

> > Why not just hack a laser pointer ? Dirt cheap
>
> Oh I would, but this is an art project that I've beeen comissioned
> to make. So I have a budget of about $100US for the laser module
> but also I have to think about the long-term maintanance of the
> project

Well, far be it from me, but ........ ;-)

You're making an assumption about what will be available in
10 years time. US Lasers could be long gone by then. I daresay
something else will be available, but according to Sod's Law it
will be just different enough to be annoying

> Unfortunately that means that potentially unreliable things like
> hacking a laser pointer are out

Reliability is the responsibility of the workman !!! ;-)) If you
build within spec and have a good margin there's no reason
to think any unit would fail prematurely. And you document
it yourself so that someone in 10 years time will have no trouble
fixing it

> It's gotta be off the shelf and documented, so that in 10 years
> when the laser craps out it'll be easy to replace with another one

If you're considering PWMing the one you get, is that any less
"hacking" than taking a cheap pointer and doing the same ?

I've looked at modules available from RS and their prices are
way higher than you'd pay at a stationary supplier for basically
the same thing sold as a pointer. Eventually I got some LM3s
from Oatley in Australia and they work great

I wonder though if 5mW is going to be enough. (I notice Digikey
describe the 38-1010-ND as "4.8MW" but I'm guessing that
should be mW !!!). 20mW might be more like it if the display
starts getting big and the dot has to move around a lot

>Does anyone know where I can get some very simple to use red laser diode
>module units? Essentially I want a off the shelf laser pointer that I
>can power with 5v. (or some other easy to produce voltage)

There are plenty of manufacturers of OEM laser modules at pretty much every price & performance
point.

If you want good beam shape you are probably looking at something a bit better engineered than a
laser pointer, but may be significantly more expensive.
If you want really good beam quality, don't rule out a surplus helium-neon tube - these are
available pretty cheaply

>I've already tried the two modules from http://www.us-lasers.com/
>(ordered through digikey, 38-1010-ND and 38-1003-ND) They are almost
>exactly what I need except for two annoying issues. First of all they
>require very precisely regulated voltage to them, I spoke to one of
>their engineers and he said that their input voltage must be exactly
>3.0V +- about 0.1 of a volt, doable, but a pain. Secondly the quality of
>the laser dot is rather poor, it's an unfocused oval rather than a tight
>round point.

What's so hard about a 3V regulator..? 0.1V is trivially easy with a regulator chip.

>> Why not just hack a laser pointer ? Dirt cheap
>
>Oh I would, but this is an art project that I've beeen
>comissioned to make. So I have a budget of about $100US
>for the laser module but also I have to think about the
>long-term maintanance of the project. Unfortunately
>that means that potentially unreliable things like
>hacking a laser pointer are out. It's gotta be off the
>shelf and documented, so that in 10 years when the laser
>craps out it'll be easy to replace with another one.

To me this is all the more reason to hack a laser pointer. If you go out and
buy a specific laser unit then replacement is all the more awkward in 10
years, as technology moves on and things are done in a different way.

But a Laser Pointer in a pen type barrel will probably still be available -
for the same use as laser pointers are now. If you can fit a laser pointer
by mounting the barrel with minimum modifications and supply a suitable
voltage to it to replace the batteries, then whenever it fails the same can
probably be done with whatever is available then.

On Tue, Dec 20, 2005 at 11:21:10PM +1300, Jinx wrote:
> > > Why not just hack a laser pointer ? Dirt cheap
> >
> > Oh I would, but this is an art project that I've beeen comissioned
> > to make. So I have a budget of about $100US for the laser module
> > but also I have to think about the long-term maintanance of the
> > project
>
> Well, far be it from me, but ........ ;-)
>
> You're making an assumption about what will be available in
> 10 years time. US Lasers could be long gone by then. I daresay
> something else will be available, but according to Sod's Law it
> will be just different enough to be annoying

Definetely one of my worries. I mean, by asking for such modules, what
I'm really thinking is are they commonly available? Because if they are
now, there's a good chance that they'll be available in 10 years, even
if not specifically from US Lasers.

> > Unfortunately that means that potentially unreliable things like
> > hacking a laser pointer are out
>
> Reliability is the responsibility of the workman !!! ;-)) If you
> build within spec and have a good margin there's no reason
> to think any unit would fail prematurely. And you document
> it yourself so that someone in 10 years time will have no trouble
> fixing it

You're right for sure, but I guess my point is that that $1 laser
pointer you get from a surplus place doesn't *have* specs to follow.

> > It's gotta be off the shelf and documented, so that in 10 years
> > when the laser craps out it'll be easy to replace with another one
>
> Seriously, what makes "off the shelf" so dependable ? I've had
> my share of garbage OTS, and I'm sure everyone else here has.

As I say above, at least the OTS stuff *has* specs to follow, even if
they lie and the hardware doesn't meet the specs. Makes me look less bad
too!

> If you're considering PWMing the one you get, is that any less
> "hacking" than taking a cheap pointer and doing the same ?

Not if the datasheet mentions PWM and I check it over with one of their
engineers. :)

> I've looked at modules available from RS and their prices are
> way higher than you'd pay at a stationary supplier for basically
> the same thing sold as a pointer. Eventually I got some LM3s
> from Oatley in Australia and they work great
>
> http://www.oatleyelectronics.com/lasers.html

Thansk for the tip, looks like a decent module, and nice price!

> Oatley also sell lenses (collimating and line, plastic, they're OK)
>
> I wonder though if 5mW is going to be enough. (I notice Digikey
> describe the 38-1010-ND as "4.8MW" but I'm guessing that
> should be mW !!!). 20mW might be more like it if the display
> starts getting big and the dot has to move around a lot

It's going to be stationary actually. See, what I'm doing is mounting
the laser to the shaft of a stepper motor. Then I *very* slowly pan it
across a wall. Each 12 hour period the laser dot will make one trip from
one side of the wall to the other. The whole assembly is mounted into
the ceiling of a room and some control lines and power is run behind the
wall to a control panel somewhere. The only tricky part is microstepping
the motor for a sufficiently high resolution, I have a 400 step/rev
motor I'm using with 64x microstepping. Actual realised resolution seems
to be maybe 1600steps/rev.

On Tue, Dec 20, 2005 at 12:28:22PM +0000, Mike Harrison wrote:
> On Tue, 20 Dec 2005 04:14:05 -0500, you wrote:
>
> >Does anyone know where I can get some very simple to use red laser diode
> >module units? Essentially I want a off the shelf laser pointer that I
> >can power with 5v. (or some other easy to produce voltage)
>
> Have a look at
> http://www.roithner-laser.com/

Thanks! That's a great link, looks like I've got a lot of possibilities
to choose from. It's interesting that the barrel sizes seem to be
somewhat standardized too, in light of this I'll probably make my
mechanical mount for the pointer to have an insert so that any barrel
size can be mounted by swapping inserts.

> There are plenty of manufacturers of OEM laser modules at pretty much every price & performance
> point.
>
> If you want good beam shape you are probably looking at something a bit better engineered than a
> laser pointer, but may be significantly more expensive.
> If you want really good beam quality, don't rule out a surplus helium-neon tube - these are
> available pretty cheaply

It would be nice to look at that's for sure... But no, anything good
enough to be used as a laser pointer will be fine. As I explained to
another poster the laser dot is not moving quickly or used to "draw",
just to indicate.

> >I've already tried the two modules from http://www.us-lasers.com/
> >(ordered through digikey, 38-1010-ND and 38-1003-ND) They are almost
> >exactly what I need except for two annoying issues. First of all they
> >require very precisely regulated voltage to them, I spoke to one of
> >their engineers and he said that their input voltage must be exactly
> >3.0V +- about 0.1 of a volt, doable, but a pain. Secondly the quality of
> >the laser dot is rather poor, it's an unfocused oval rather than a tight
> >round point.
>
> What's so hard about a 3V regulator..? 0.1V is trivially easy with a regulator chip.

Oh it's pretty easy, heck, I've been running the us-laser pointer for
awhile now while developing the PIC control hardware and software using
a standard lm314. (or whatever the # is)I'm just thinking long term it'd
make things easier, especially if the laser module has to be changed. I
won't be around to do it!

Looks like what I'll do in any case is supply power to the laser module
with a adjustable regulator to make it easy to adapt to the requierments
of whatever laser module gets used in the future. Just change a trim pot
setting.

> > Does anyone know where I can get some very simple to use red
> > laser diode module units ?
>
> Why not just hack a laser pointer ? Dirt cheap

I used laser pointer modules from Radio Shack, of all places, a few
years ago in my senior design project. IIRC, they were about $6,
and were basically a regular ol' laser pointer with two wires out the
back.

We looked at hacking laser pointers, but getting into the case
ended up being such a PITA it wasn't worth it. AND the Radio
Shack modules were as cheap, to boot!

The nice thing is that these are coil actuated, so if the timing isn't
right, rip out the circuit, and pulse the coil yourself. Put it on
the hour hand. The second hand is moved 1/60 rev each pulse, the
minute hand goes 1/3600 rev per pulse, and hour hand 1/216,000 rev per
pulse.

The advantage above a micro-stepping stepper motor is that you don't
need current between pulses, and in fact you could run the whole
assembly off a AA cell for the year. Not to mention much higher
resolution and accuracy than the microstepping stepper. Not that it
matters much since you're running the laser continuously...

Perhaps there are other constraints that this doesn't meet, but the
high-torque clock in the link above may be worth considering. If it
doesn't have a spot for a second hand, it is likely that the gears
still provide 1/216,000 rev per pulse to the hour hand so the circuit
is the same for all the clock modules.

> On Tue, Dec 20, 2005 at 11:21:10PM +1300, Jinx wrote:
> > I wonder though if 5mW is going to be enough. (I notice Digikey
> > describe the 38-1010-ND as "4.8MW" but I'm guessing that
> > should be mW !!!). 20mW might be more like it if the display
> > starts getting big and the dot has to move around a lot
>
> It's going to be stationary actually. See, what I'm doing is mounting
> the laser to the shaft of a stepper motor. Then I *very* slowly pan it
> across a wall. Each 12 hour period the laser dot will make one trip from
> one side of the wall to the other. The whole assembly is mounted into
> the ceiling of a room and some control lines and power is run behind the
> wall to a control panel somewhere. The only tricky part is microstepping
> the motor for a sufficiently high resolution, I have a 400 step/rev
> motor I'm using with 64x microstepping. Actual realised resolution seems
> to be maybe 1600steps/rev.
>

With many of these laser pointers, the metal case of the laser module itself
is connected to the positive supply. I used a bunch of Alpec units in a
project last year & had to run them with a -3 Volt supply because the mounts
they were to be put into were at PSU ground.

These cheap laser units will often die if the supply is shorted out. I'm not
sure why this is, it may be transients on the supply when the short is taken
off? They do seem to be quite sensitive to the supply voltage. The diode
itself is powered from a current regulated by feed back fron a photo diode
inside the laser. With cheap units like these, designed to be run from
batteries, you can be sure that the current regulator circuit is not over
engineered.

>On Tue, Dec 20, 2005 at 10:08:22PM +1300, Jinx wrote:
>
>
>>>Does anyone know where I can get some very simple to use red
>>>laser diode module units ?
>>>
>>>
>>Why not just hack a laser pointer ? Dirt cheap
>>
>>
>
>Oh I would, but this is an art project that I've beeen comissioned to
>make. So I have a budget of about $100US for the laser module but also I
>have to think about the long-term maintanance of the project.
>Unfortunately that means that potentially unreliable things like hacking
>a laser pointer are out. It's gotta be off the shelf and documented, so
>that in 10 years when the laser craps out it'll be easy to replace with
>another one.
>
>
>

So what would be wrong with buying 10 of the $1 laser pointers, hacking
all of them to fit the project and keeping them on hand as long as you
are around to repair it or include them as spares in the deal.

On Tue, Dec 20, 2005 at 09:45:50AM -0500, M. Adam Davis wrote:
> I suppose there's a reason you're not simply using the hour hand from
> a strong clock module?
>
> www.klockit.com/products/dept-157__sku-AAAAG.html
>
> The nice thing is that these are coil actuated, so if the timing isn't
> right, rip out the circuit, and pulse the coil yourself. Put it on
> the hour hand. The second hand is moved 1/60 rev each pulse, the
> minute hand goes 1/3600 rev per pulse, and hour hand 1/216,000 rev per
> pulse.
>
> The advantage above a micro-stepping stepper motor is that you don't
> need current between pulses, and in fact you could run the whole
> assembly off a AA cell for the year. Not to mention much higher
> resolution and accuracy than the microstepping stepper. Not that it
> matters much since you're running the laser continuously...

Yeah, this will be wired to mains current. Though I do plan to add a
supercap to power the PIC only for short power outages. I've done that
once before for another clock powered off of a doorbell circuit and it's
been tolerating about 10 power outages a day from people ringing the
doorbell for months now with no problem. I just made it possible to have
it detect when it's running off of the capacitor by isolating the PIC's
Vcc from the rest of the circuit with a diode, then added a connection
to the normal power to an IO line, the second the PIC detects that IO
line go low it drastically reduces it's oscillator speed to go into
low-power mode.

As for why you'd power a clock from a doorbell circuit? Well, it's an
old house, and I wasn't allowed to touch anything more than a small
segment of the drywall, so no running power lines anywhere. Easiest just
to tap off of the doorbell as I was installing the device by the front
door!

> Perhaps there are other constraints that this doesn't meet, but the
> high-torque clock in the link above may be worth considering. If it
> doesn't have a spot for a second hand, it is likely that the gears
> still provide 1/216,000 rev per pulse to the hour hand so the circuit
> is the same for all the clock modules.

Hmm... That's actually a really interesting idea. One problem I see is
that I need some method of reversing the mechanism when at the end of
the 12 hour period, the laser needs to track back to the starting
position. Still that could work rather well for some other clock designs
I have... I've got metalworking equipment sure, but building gear trains
takes lots of work!

On Tue, Dec 20, 2005 at 09:08:06AM -0600, R. I. Nelson wrote:
> >Oh I would, but this is an art project that I've beeen comissioned to
> >make. So I have a budget of about $100US for the laser module but also I
> >have to think about the long-term maintanance of the project.
> >Unfortunately that means that potentially unreliable things like hacking
> >a laser pointer are out. It's gotta be off the shelf and documented, so
> >that in 10 years when the laser craps out it'll be easy to replace with
> >another one.
> >
> >
> >
> So what would be wrong with buying 10 of the $1 laser pointers, hacking
> all of them to fit the project and keeping them on hand as long as you
> are around to repair it or include them as spares in the deal.

I was considering that. But then someone needs to keep track of those
laser pointers, and unfortunately they'll probably get lost. As it is
I'm going to do my best to keep the unit "self-documenting", so for
instance every important connection is labeled as to what it is and what
voltages it expects. I'll give the client a copy of the schematics and
source code also. Finally I'm burning an offering to the FLASH gods to
try to make sure my PIC chips flash memory doesn't die in 20 years. :)

On Tue, Dec 20, 2005 at 03:02:21PM -0000, Joe McCauley wrote:
> With many of these laser pointers, the metal case of the laser module itself
> is connected to the positive supply. I used a bunch of Alpec units in a
> project last year & had to run them with a -3 Volt supply because the mounts
> they were to be put into were at PSU ground.

!!! Thanks for the heads up! Looks like the case will be plastic then.
I'm lucky I can easilly isolate it electrically.

> These cheap laser units will often die if the supply is shorted out. I'm not
> sure why this is, it may be transients on the supply when the short is taken
> off? They do seem to be quite sensitive to the supply voltage. The diode
> itself is powered from a current regulated by feed back fron a photo diode
> inside the laser. With cheap units like these, designed to be run from
> batteries, you can be sure that the current regulator circuit is not over
> engineered.

Definetely. I've read through Sam's Laser FAQ on the subject, aparently
most of the cheap laser pointer's except the battery to do most of the
current regulation. The laser diodes are then engineered to tolerate a
fairly wide range of currents/voltages compared to standard diodes.
Very, very cheap indeed.

> I was considering that. But then someone needs to keep track of those
> laser pointers, and unfortunately they'll probably get lost. As it is
> I'm going to do my best to keep the unit "self-documenting", so for
> instance every important connection is labeled as to what it is and what
> voltages it expects. I'll give the client a copy of the schematics and
> source code also. Finally I'm burning an offering to the FLASH gods to
> try to make sure my PIC chips flash memory doesn't die in 20 years. :)

Any reason not to just stick the extra laser pointers in the unit's case?

You don't need to mount the laser on the shaft of the stepping motor.
All you need is a tiny mirror mounted on the end of the shaft at 45
degrees. Point the laser into it, i.e. along the axis of the motor,
and it will scan the beam through 360 degrees if you want. This will
also work with a clock movement, even a very small one. The mirror
only needs to be big enough to intercept the laser. This lets you use
any laser.

Meredith instruments is a source of good quality modules. You can get
one with a built in collimating lens, and a good long lifetime.

>> Perhaps there are other constraints that this doesn't meet, but the
>> high-torque clock in the link above may be worth considering. If it
>> doesn't have a spot for a second hand, it is likely that the gears
>> still provide 1/216,000 rev per pulse to the hour hand so the circuit
>> is the same for all the clock modules.
>
>Hmm... That's actually a really interesting idea. One problem I see is
>that I need some method of reversing the mechanism when at the end of
>the 12 hour period, the laser needs to track back to the starting
>position.

How about a 2-sided Mirror on the clock mechanism reflecting the beam from a stationary laser, so it
gives a 180 deg sweep for each 12 hour period (clock mech driven at half speed to give 1 rotation
every 24 hrs)

Not just if it is moving slowly. It will need to be mounted so that it is
impossible for anyone to look into the beam at any time. This will probably
include needing to mount it so someone cannot reach it with a pocket mirror
to re-direct the beam somewhere else.

On Tue, Dec 20, 2005 at 11:03:04AM -0500, William Couture wrote:
> > I was considering that. But then someone needs to keep track of those
> > laser pointers, and unfortunately they'll probably get lost. As it is
> > I'm going to do my best to keep the unit "self-documenting", so for
> > instance every important connection is labeled as to what it is and what
> > voltages it expects. I'll give the client a copy of the schematics and
> > source code also. Finally I'm burning an offering to the FLASH gods to
> > try to make sure my PIC chips flash memory doesn't die in 20 years. :)
>
> Any reason not to just stick the extra laser pointers in the unit's case?

The case has got to fit inside a ceiling with 2 inches of usable depth.
:( I also need to keep the length and width to a minimum by order of the
client.

That said... I could probably get away with sticking them in a ziplock
bag and hiding them next to the case! Maybe I'll do that for at least
the documentation for the work, schematics and sourcecode. PIC chips
probably won't be available in 20 years, but that'll at least tell
peopel what the pieces behavior was. In the art world it's considered ok
to replace the "brains" of an electronic work so long as it's not
visible to the viewer, so make the behavior the same.

> Secondly the quality of
> the laser dot is rather poor, it's an unfocused oval rather than a tight
> round point.
>
> Something like one of those modules but that can accept less tightly
> regulation power and has a good quality dot would be perfect. Anyone
> here dealt with this sort of thing before?

Hi Peter,

There seem to be a lot of replies, I hope this message doesn't get lost in
all the noise.

I have lots of experience with lasers. The output from a laser diode is an
oval. It is usually about 4:1 although some newer and more expensive
diodes are 2:1. The usual way to make it round is to clip the beam. There
is a company that makes laser diodes with circular correcting optics
inside although you pay dearly for it:http://www.blueskyresearch.com/index.htm
The diodes are called CircuLaser. If you want the best beam quality, start
with one of these. They also sell laser modules but I have no experience
with those.

Any red laser module decently constructed should have a very long lifetime
- green is where the reliability would be more of an issue.

Peter Todd wrote:
> I was considering that. But then someone needs to keep track of those
> laser pointers, and unfortunately they'll probably get lost.

I strongly suspect that, in 10 years, the "laser module" will have
changed some minor-to-them but major-to-you component.

I'd go with the laser pen idea, and buy 25 of them. Strap them to the
inside of the top of the case like spare fuses, and let people just snap
them in, like spare fuses. The ones I hacked up no longer have most of
the body preent, but that leaves a very nicely sealed can for the
average non-geek to pull out and snap in as needed.

> On Tue, Dec 20, 2005 at 09:45:50AM -0500, M. Adam Davis wrote:
> > www.klockit.com/products/dept-157__sku-AAAAG.html
> > Perhaps there are other constraints that this doesn't meet, but the
> > high-torque clock in the link above may be worth considering. If it
> > doesn't have a spot for a second hand, it is likely that the gears
> > still provide 1/216,000 rev per pulse to the hour hand so the circuit
> > is the same for all the clock modules.
>
> Hmm... That's actually a really interesting idea. One problem I see is
> that I need some method of reversing the mechanism when at the end of
> the 12 hour period, the laser needs to track back to the starting
> position. Still that could work rather well for some other clock designs
> I have... I've got metalworking equipment sure, but building gear trains
> takes lots of work!
>

>> It's going to be stationary actually. See, what I'm doing is mounting
>> the laser to the shaft of a stepper motor. Then I *very* slowly pan it
>> across a wall. Each 12 hour period the laser dot will make one trip from
>> one side of the wall to the other. The whole assembly is mounted into
>> the ceiling of a room and some control lines and power is run behind the
>> wall to a control panel somewhere. The only tricky part is microstepping
>> the motor for a sufficiently high resolution, I have a 400 step/rev
>> motor I'm using with 64x microstepping. Actual realised resolution seems
>> to be maybe 1600steps/rev.

How accurate does it have to be (as in f.s. and repeating) ? Gluing a
small mirror on the bent needle of an analog meter should help you here.
A 50uA f.s. scale meter would likely need only half that current on
average. 25uA is very nice for battery power. The meter can be driven by
a single PWM channel. It could work with about 18mAh for a month. Two AA
cells contain a hundred times more energy than that.

Use a good quality multi-turn if you're worried about drift. Also
you can coarse-tune the voltage with fixed resistors and fine-
tune it with a lower value trimmer, eg instead of a 100k pot for
the whole range, you might have a 5k pot between a 68k and
a 33k

Neil Baylis wrote:
> You don't need to mount the laser on the shaft of the stepping motor.
> All you need is a tiny mirror mounted on the end of the shaft at 45
> degrees. Point the laser into it, i.e. along the axis of the motor,
> and it will scan the beam through 360 degrees if you want.<snip>
IIRC, the mirror should be a front surface mirror (the reflecting
surface is on the front of the glass), or you will get ghosting and
distortion from the laser. Some medical laser imagers (to expose film
from a digital source - eg Kodak DryView 8900) use a tilted 6 sided
front surface mirror that spins to trace across the film while it drives
through (like a raster scan).
Laser alignment tools for doing suspended ceiling tile spin a mirror to
put a red line around the room at the same height, and some of the
inexpensive laser leveling tools seem to have fairly bright lasers in
them.....

> It's gotta be off the shelf and documented, so that in 10 years when
> the laser craps out it'll be easy to replace with another one.
>

"off the shelf and documented" is an entirely different problem than
"the same part will still be available in 10 years." The latter is
MUCH harder to find. This is a major PITA when trying to use OTS
PCs or PC components for an embedded design with a long lifetime;
THOSE parts tend to disappear in a year or two, never to be seen
again, perhaps with any driver SW that existed disappeared as well.

I don't think that red laser modules have enough 'real' applications
that there's been any standardization of form factors or pin-outs or
any of that; you'll just have to take your chances...

>How about a 2-sided Mirror on the clock mechanism
>reflecting the beam from a stationary laser, so it
>gives a 180 deg sweep for each 12 hour period
>(clock mech driven at half speed to give 1 rotation
>every 24 hrs)

hey we do that on our space craft instrument to scan the earth each rotation
of the craft.

you could also put your trim pot across another resistor in parralel
so if you wanted ~25K
say a 50K R and a 100K trim pot at 50%
any drift in your trim is halved
(same in your R)
a smaller R and bigger Trim will reduce your trim drift effect too.

On Tue, Dec 20, 2005 at 08:54:08AM -0800, Bob Blick wrote:
> There seem to be a lot of replies, I hope this message doesn't get lost in
> all the noise.
>
> I have lots of experience with lasers. The output from a laser diode is an
> oval. It is usually about 4:1 although some newer and more expensive
> diodes are 2:1. The usual way to make it round is to clip the beam. There
> is a company that makes laser diodes with circular correcting optics
> inside although you pay dearly for it:
> http://www.blueskyresearch.com/index.htm
> The diodes are called CircuLaser. If you want the best beam quality, start
> with one of these. They also sell laser modules but I have no experience
> with those.

Ahh, that explains a lot! The nice circular point laser pointers I have
are probably the "clipping" type, I've noticed they always place a round
hole some distance away from the diode assembly...

On Tue, Dec 20, 2005 at 08:12:06AM -0800, Neil Baylis wrote:
> You don't need to mount the laser on the shaft of the stepping motor.
> All you need is a tiny mirror mounted on the end of the shaft at 45
> degrees. Point the laser into it, i.e. along the axis of the motor,
> and it will scan the beam through 360 degrees if you want. This will
> also work with a clock movement, even a very small one. The mirror
> only needs to be big enough to intercept the laser. This lets you use
> any laser.

As someone else mentioned I'll need a front-silvered mirror for that. I
thought of this option initially, and decided against it as the mirror
would eventually get dusty. Cleaning is problimatic as it's high up on a
ceiling and would requier special training.

I wonder though... Is there such a thing as a "pseudo-half-silvered"
mirror? Make one that applys the silver to a glass carrier and then
applies a very thin protective film to the silver. While there still
would be two reflections present they could be very close to each other,
making the resulting beam be for all practical purposes a single beam.

> Meredith instruments is a source of good quality modules. You can get
> one with a built in collimating lens, and a good long lifetime.

Good resource! Their 650nm 3.5mW is cheap too, only $20. At 3.5mW it's
about the brightness I want, as described below...

> Be careful with safety issues if the beam is moving slowly.

Well I plan to use a very *low-powered* laser. One that is (relatively)
eye-safe. Most laser pointers are such that if you look at one, even
star at one, you are only temporarily blinded. That level of safety is
exactly what I want. 3.5mW might just give that to me... :)

On Tue, Dec 20, 2005 at 10:38:07PM -0800, William Chops Westfield wrote:
>
> > It's gotta be off the shelf and documented, so that in 10 years when
> > the laser craps out it'll be easy to replace with another one.
> >
>
>
> "off the shelf and documented" is an entirely different problem than
> "the same part will still be available in 10 years." The latter is
> MUCH harder to find. This is a major PITA when trying to use OTS
> PCs or PC components for an embedded design with a long lifetime;
> THOSE parts tend to disappear in a year or two, never to be seen
> again, perhaps with any driver SW that existed disappeared as well.
>
> I don't think that red laser modules have enough 'real' applications
> that there's been any standardization of form factors or pin-outs or
> any of that; you'll just have to take your chances...

Actualy I disagree on that. Practically every laser module I've seen has
a number of things in common:

Cylindrical case > 5mm in dia < 30 mm in dia.

I can handle this by making the mount have a removable liner to adapt to
the size of the pointer. If a new one needs to be made, chances are in
10 years 3d printing technology will make that job much easier than it
is now!

Minimum voltage required from 3V to 6V

So I'll just put a easilly adjustable pot to change that as needed.
Current is always less than 500mA and probably will be for any eye-safe
laser!

Pin-outs? You mean one wire is black and one is red?

Seriously, they are all simple power devices. Some of the odder ones
have adjustable brightness with a third lead, but I think
non-adjustables will always be available.

Nah, the laser doesn't worry me too much, other then the annoying issue
of them probably burning out after 10,000 hours. In the very long term
flash memory is going to die which means that we run into the fun issue
of drive SW and dev kit availability as you so accurately mentioned.
That's the real killer. The one that will force an expensive
reimplementation of the elctronics is 30-50 years time.

I'll probably be alive too to regret all the dumb choices I made when I
get the warrenty call. :)

>
> As someone else mentioned I'll need a front-silvered mirror for that. I
> thought of this option initially, and decided against it as the mirror
> would eventually get dusty. Cleaning is problimatic as it's high up on a
> ceiling and would requier special training.

In an application of a turning infrared temperature sensor I saw the dust
has been caught with a high voltage electrode.

>> As someone else mentioned I'll need a front-silvered mirror for
>> that. I
>> thought of this option initially, and decided against it as the
>> mirror
>> would eventually get dusty. Cleaning is problimatic as it's high up
>> on a
>> ceiling and would requier special training.

> In an application of a turning infrared temperature sensor I saw the
> dust
> has been caught with a high voltage electrode.

A negative ion generator may also be useful. Similar effect but
perhaps more aggressive as it actively attempts to cast ions adrift.

> >> As someone else mentioned I'll need a front-silvered mirror for
> >> that. I
> >> thought of this option initially, and decided against it as the
> >> mirror
> >> would eventually get dusty. Cleaning is problimatic as it's high up
> >> on a
> >> ceiling and would requier special training.
>
> > In an application of a turning infrared temperature sensor I saw the
> > dust
> > has been caught with a high voltage electrode.
>
> A negative ion generator may also be useful. Similar effect but
> perhaps more aggressive as it actively attempts to cast ions adrift.

As long as the mirror isn't seen as more positive than the ions, in which case it will be dusted-over pretty
quickly! I had a negative ion generator in my bedroom, and anything plastic (mains plugs and sockets for
example) within a few feet of it was covered in a fine dust within a week.

On Fri, Dec 23, 2005 at 01:37:59PM +0000, Howard Winter wrote:
> > A negative ion generator may also be useful. Similar effect but
> > perhaps more aggressive as it actively attempts to cast ions adrift.
>
> As long as the mirror isn't seen as more positive than the ions, in which case it will be dusted-over pretty
> quickly! I had a negative ion generator in my bedroom, and anything plastic (mains plugs and sockets for
> example) within a few feet of it was covered in a fine dust within a week.

And while the mirror wouldn't be more positive, if I'm correct the laser
sure will be as all these laser modules have a positive case... Some of
that dust would probably get to obstruct the lens in the laser soon
enough.

> On Tue, Dec 20, 2005 at 08:12:06AM -0800, Neil Baylis wrote:
>> You don't need to mount the laser on the shaft of the stepping motor.
>> All you need is a tiny mirror mounted on the end of the shaft at 45
>> degrees. Point the laser into it, i.e. along the axis of the motor,
>> and it will scan the beam through 360 degrees if you want. This will
>> also work with a clock movement, even a very small one. The mirror
>> only needs to be big enough to intercept the laser. This lets you use
>> any laser.
>
> As someone else mentioned I'll need a front-silvered mirror for that. I
> thought of this option initially, and decided against it as the mirror
> would eventually get dusty. Cleaning is problimatic as it's high up on a
> ceiling and would requier special training.

You do not need a front silvered mirror. The double reflexion produced
by the usual mirror is not a problem as it is weak (<10%) of the main
beam and very close to it (at most sqrt(glass thickness) for angles of
+/-45 degrees).

You may also want to give up on the stepper and use an analog 50uA meter
movement from an analog DVM. You can glue the mirror on that and drive
it with PWM from a pic as I said.

You may find that the stepper will not be able to stop on positions you
like. For a reasonable sized room even a 0.5 degree per step stepper
will cause your spot to stop far away from any reasonable-sized stops on
a wall. The analog movement can be driven with say 16-bit pwm and will
easily be settable for such situations.

>I wonder though... Is there such a thing as a
>"pseudo-half-silvered" mirror? Make one that applys
>the silver to a glass carrier and then applies a very
>thin protective film to the silver. While there still
>would be two reflections present they could be very
>close to each other, making the resulting beam be for
>all practical purposes a single beam.

The descan mirrors used in the space craft instruments I am dealing with are
done this way. I do not know what the protective coating over the silver is,
but there is certainly an extremely thin coating on top of the silver to
protect from tarnishing while still earth bound.

I suspect that if you went out and purchased a front silvered mirror, it
would come with such a coating as a normal finish.

> You do not need a front silvered mirror. The double reflexion produced
> by the usual mirror is not a problem as it is weak (<10%) of the main
> beam and very close to it (at most sqrt(glass thickness) for angles of
> +/-45 degrees).

still in the same thread: I know it's possible to PWM a laser diode
or a laser diode module (just because I've done that) but how reliable
it would be? There are any tricks to not shorten the diode life?

> My question: What exactly the circuit on the PCB of a laser diode
> module does? It seens to be a simple current regulator.

Could be, if it's a two-legged diode. Three-legged diodes have a monitor
photodiode so you can build a closed loop circuit.

> There are some *cheap* way of measuring 635nm and 532nm laser beam
> power?

Solar cell works quite well.

But wait, you mention 532nm. That's a completely different animal. There
is no 532nm "diode". They are all diode pumped. 880nm diode pumps a 1064nm
laser, then frequency doubled. Expensive, inefficient, and extrememly
sensitive to temperature.

> still in the same thread: I know it's possible to PWM a laser diode
> or a laser diode module (just because I've done that) but how reliable
> it would be? There are any tricks to not shorten the diode life?

Just don't exceed the ratings of the diode. And remember that the diode
can be damaged by excessive optical output, not just excessive current.